<template>
    <ul class="list">
        <li class="item" v-for="item of letters" :key="item" :ref="item" @touchstart.prevent="handleTouchStart"
            @touchmove="handleTouchMove" @touchend="handleTouchEnd" @click="handleLetterClick">
            {{ item }}
        </li>
    </ul>
</template>

<script>
export default {
    name: 'CityAlphabet',
    props: {
        cities: Object
    },
    computed: {
        letters() {
            const letters = []
            for (let i in this.cities) {
                letters.push(i)
            }
            return letters //['A','B','C']
        }
    },
    data() {
        return {
            touchStatus: false,
            startY: 0,
            timer: null //节流阀
        }
    },
    updated() {
        this.startY = this.$refs['A'][0].offsetTop //页面数据更新时
    },
    methods: {
        handleLetterClick(e) {
            this.$emit('change', e.target.innerText)
        },
        handleTouchStart() {
            this.touchStatus = true
        },
        handleTouchMove(e) {
            // 可以移动
            if (this.touchStatus) {
                if (this.timer) {
                    clearTimeout(this.timer)
                }
                this.timer = setTimeout(() => {
                    const touchY = e.touches[0].clientY - 79
                    const index = Math.floor((touchY - this.startY) / 20)
                    if (index >= 0 && index < this.letters.length) {
                        this.$emit('change', this.letters[index])
                    }
                }, 8)
            }
        },
        handleTouchEnd() {
            this.touchStatus = false
        }
    }
}
</script>

<style lang="stylus" scoped>
  @import '~styles/varibles.styl'
  .list
    display: flex
    flex-direction: column
    justify-content: center
    position: absolute
    top: 1.58rem
    right: 0
    bottom: 0
    width: .4rem
    .item
      line-height: .4rem
      text-align: center
      color: $bgColor
</style>
